The invention relates to a method and an apparatus for receiving mass-produced articles or products for stacking, especially plastic cups, which after having been formed in a moulding and/or punching machine are ejected from same. The apparatus comprises a catching device assigned to the machine for receiving the products after they leave the machine and a stacking and holding device located downstream of the catching direction, in which the products are received and after stacking held ready for further transport. The catching and the stacking and holding devices are capable of being moved towards one another and away from one another. The invention relates further to a stacking and holding device suitable for use in the receiving apparatus, which comprises at least one stacking channel and one or more claw elements which run parallel with the stacking channel, surround the latter and are provided on their inner side facing the stacking channel with one or more gripping pawls adjustable rotationally and/or translationally for the grasping of mass-produced articles, especially plastic cups. The invention relates further to a gripping pawl suitable for use in the stacking device, which possesses an inner side assigned to a product or item for stacking and a rearward outer side, wherein there are formed on the inner side one or more undercuts, steps or depressions as claw elements or shear means for the product or item for stacking.
In the manufacture of plastic cups by the deep-drawing process, the use of polystyrene as a material is known. The latter is increasingly being replaced by polypropylene, which is available as a low-price material, but is more difficult to process. An article made from the latter does not acquire its final strength until hours after its manufacture. It is therefore particularly important that the xe2x80x9csoftxe2x80x9d articles ejected from the machine are as far as possible protected against mechanical forces in the axial and radial direction during the subsequent stacking operation.
For the producing of deep-drawn parts of such thermo-plastic material, in particular cups or other receptacles, an apparatus for the moulding, punching and stacking of said parts is known (German utility model 91 08 344.3). After the moulding of the plastic part the mould is opened and the plastic part is pushed into a stacking apparatus. In order to ensure a reliable transfer of the articles into the stacking apparatus, the mould is swivelled and opened, and the stacking apparatus is moved towards the Mould. It is disadvantageous here that the last plastic part ejected, which is still hot and therefore easily deformable, has to displace axially the plastic parts already stacked within the stacking apparatus. Hence a deformation of the last part ejected and received in the stacking apparatus is easily possible. For example, deformed plastic parts of an oval shape can be printed on later only with difficulty, since they can cause friction in the printing machine, something which causes fault messages.
DE 36 24 638 C2 discloses a retaining apparatus for a stacking channel, in which lids for plastic receptacles are held by means of guide rods bounding the stacking channel. The retaining apparatus is distinguished by pawls which are integral with the guide rods and are spring-mounted radially by means of compression springs. The front side of the spring-mounted pawls faces the inside of the stacking channel and consists of flat flanks which are arranged in saw-tooth-like sequence, such that there form in the area of the deeper parts of said flanks projections running in transverse direction for the edges of the lids to be held. However, the projections lie diametrically opposite one another so that bottlenecks are formed which lead to a distortion of the lids. Moreover, nothing is disclosed as to how the lids are transferred out of a mould and introduced into the stacking channel. A further disadvantage consists in the fact that the last lid to arrive in the stacking channel has to give a push to the preceding lid, which reduces the dimensional stability considerably, since a strong mechanical pressure is thereby exerted on the last lid introduced, which is still hot and hence deformable.
DE 32 37 943 A1 discloses a magazine for the stacking of paper articles, in which there are arranged on at least one guide side of the magazine, as guide surfaces, oblique surfaces succeeding one another after the manner of scales. The oblique surfaces constrict the guide shaft in the guide direction and are intended to prevent the thin sides of the paper articles, for which a wedge shape is assumed, preceding the thick sides in the guide direction. Here again nothing is inferable about the take-over of the paper articles out of a mould or similar.
DE 44 36 531 C1 discloses a method for converting particles formed and punched out of a thermo-plastic film in several rows into single-row stacks. Cups formed out of thermo-plastic film are placed in receiving spectacles by means of a vacuum transfer device. The receiving spectacle is displaced in flow direction by one row interval and then moved back again. Apparently, however, the stacks can reach only a height of three cup units.
A receiving apparatus roughly of the kind mentioned in the preamble is known from the German patent DE 195 09 057 C2. In the latter a sub-division into two steps of the transfer movement from the mould to a stacking conveyor belt is proposed, by means of which the movement time per step is,to be reduced In the first step the plastic parts, for example cups, are pushed and sucked out of the opened mould onto a first receiving plate. By swivelling of the first catching or suction plate the cups arrive with the bottom foremost at a second suction plate, where they are sucked once again. They are further blown away from the first catching or suction plate by a short blast of compressed air. While the first catching or suction plate is being swivelled back again, the second suction plate is displaced linearly together with the cup sucked on the bottom side and is lowered to an extent such that the cup may be deposited on an already assembled stack of cups. This poses an additional requirement in control terms, however, namely that the vertical movement of the second suction plate has to be reduced from one cycle to the next, because the stack grows in its height. The swivelling of the first catching and suction plate also poses an additional requirement in construction terms. It is a further complication that the movements of the first catching and suction plate and of the second suction plate have to be coordinated or synchronised with one another, which leads to further control requirements.
The invention is based on the object of further developing a receiving method and a receiving apparatus of the kind mentioned in the preamble, while at the same time avoiding the above-mentioned disadvantages, in such a way that through careful handling of the plastic products ejected from the mould a simplification in the sequence of movements and in the equipment design is achieved. In particular the number of the transfer stations between plastic mould and stacking site and of the drive components required is to be reduced. In addition, a considerable simplification of the sequence control of the transfer components which grasp the plastic products is to be aimed for. Finally, the reliability of the taking over of the plastic products out of the mould and their stacking in the operating sequence is to be increased, in the course of which the plastic products are to be handled in a careful manner.
In order to solve this set of problems, it is proposed in the case of a receiving method for instance of the kind mentioned in the preamble that the stacking and holding device be used during the movement towards one another to grasp the product or products as they leave the catching device and during the movement away from one another to withdraw the product or products out of the catching device. The practice conventionally adopted in the prior art of operating the stacking and holding device, during the depositing of the products by the catching and transfer device, merely as a passive base or standing surface will therefore be abandoned. Instead, according to the invention, the stacking and holding device will be provided with an active role or function, namely of itself fetching the products from the catching device, after which the option of a careful stack formation then exists. The possibility is therefore further created of simplifying considerably the sequence of movements for the catching device and also the sequential control in time and synchronisation. A particular development of the invention thus consists in the fact that the moving towards and away from one another of the catching and stacking and holding devices takes place linearly and/or regularly alternately. With the linear sequence of movements a change in the alignment of the product grasped in the catching device is avoided or no longer necessary. Above all in the case of a cup shape the products may be grasped by the catching device out of the mould without a change in their movement alignment and transferred into the stacking and holding device, as well asxe2x80x94while maintaining the movement alignment out of the mouldxe2x80x94being stacked on top of one another there. It also comes within the scope of the invention, however, to combine the sequence of movements above all outside the product transfer period with non-linear, circular and/or polygonal movement paths, including turning or swivelling movements. Thus there may be imparted to the catching device, after the setting of an adequate distance from the stacking and holding device relative to the mould, a bending and/or swivelling movement.
On the basis of the general inventive idea there arises the possibility, during the movement towards one another, of using the catching device for the sliding of the product or products into the stacking and holding device. In particular, a product already located in the stacking and holding device may during or after the movement towards one another be displaced further by the catching device, in order to operate further the stacking of the products there.
As regards the receiving of freshly moulded plastic products, their cooling with retention of the specified form is problematical. In this respect it is provided according to a particularly advantageous form of the invention that the last product which has been grasped in the stacking and holding device is for the period at least of a movement away from and subsequently towards one another be prevented from making contact with previously gripped, optionally stacked products pending the gripping of a next product.
In order to solve the above set of problems there is proposed according to the invention, for a receiving apparatus with the features according to the preamble, the arrangement of gripping members singly or as a plurality on or in both the catching device and the stacking and holding device. The gripping members are formed in such a way that with the movement of the catching and stacking and holding devices towards one another and away from one another a taking over of the products by the catching device into the stacking and holding device takes place. The possibility is therefore created of the particularly advantageous development according to which the stacking and holding device may be anchored or kept still in a fixed position, for example in a machine foundation plate, while the catching device may move to and fro between the plastic mould and the stacking and holding device in a simple, preferably linear movement. On the basis of the invention the taking over and stacking process for the plastic product may be divided into two phases: taking over of the plastic product out of the tool by means of the catching device; transfer of the plastic product out of the catching device to the stacking and holding device and stacking there, wherein a bringing of the two devices closer to one another takes place.
According to a particular development of the invention the gripping members for the catching and the stacking and holding devices are formed projecting in each case. A careful transfer of the fresh plastic product reaching the stacking and holding device from the mould may be more easily secured in this way. This is promoted, in a further expression of the invention in concrete terms, by the gripping members disposed on the catching device and the gripping members disposed on the stacking and holding device being offset relative to one another. The catching and the stacking and holding devices may thereby during their movement towards and/or away from one another be mutually crossed or penetrated and/or engaged by their respective (mutually offset) gripping members. A plastic product already grasped by the catching device may thus be taken over by the penetrating gripping members of the stacking and holding device and remain there in the course of the separation.
A careful transfer of fresh and still deformable plastic products may be facilitated by the gripping members being arranged symmetrically with respect to a plane, axis, centre or other symmetry element within the catching and/or stacking and holding device, and said symmetry element lying congruent with a symmetry element of the assigned or to be grasped product. As a particular development of said concept the gripping members are arranged along a profile or plan view which corresponds to the periphery, the outline or the miscellaneous shape of the product to be received.
According to a development of the invention the gripping members are provided with suspension, clamping, locking, snap and/or hook elements, which are constructed for detachable engagement with the product to be grasped. The gripping function in the catching or the stacking and holding device may be accomplished with said elements. The above-mentioned elements are with expediency arranged at points from which they may grasp the plastic product as carefully as possible and in particular in its most robust areas and sections, for example in the case of cups the opening edge.
According to a further development of the invention the gripping elements are provided with claw, stay or barb elements or other pulling and/or shear means, so that in the course of the movement towards and/or away from one another of catching or stacking and holding device there is imparted to the grasped products a pulling, sliding or shear force in the direction from the catching to the stacking and holding device. A careful sliding onto an already existing stack of previously accepted plastic products may thereby be achieved. In particular the prevention of the disadvantage resulting from the prior art, namely that a freshly formed and taken over product has to displace a stack already formed from products taken over earlier, is supported. For the shear means may in particular be arranged staggered in such a way that for the last plastic product taken over, which is still fresh or hot, initially a certain distance is observed with respect to the stack of products taken over earlier.
In order, during the grasping of a plastic product by the gripping members, to minimise the pressure on the product as far as possible, it is provided according to a development of the invention that the above-mentioned elements or shear means, in particular if they lie on different gripping members, are arranged mutually offset in the direction of the catching to the stacking and holding device. A so-called xe2x80x9chigh-deep effectxe2x80x9d may be achieved in this way: if the above-mentioned elements or shear means project with respect to the product, but lie mutually offset in the take-over direction, the number of bottlenecks will be reduced considerably and hence the risk of deformation of the fresh and still sensitive plastic product be minimised. Said advantageous effect may be promoted still further if different gripping elements distanced from one another possess different quantities of the elements or pulling or shear means. The offset arrangement may be accomplished more easily in this way.
In order to achieve a compact and specific gripping and guiding effect above all in the catching direction, according to an advantageous development of the invention the gripping members, even if they are assigned to a product to be grasped jointly, are arranged or sub-divided into different groups. The gripping members of a group, for example of a pair or with two gripping members, possess a far smaller distance from one another than from the gripping members of another group. The gripping and guiding function may therefore be localised more intensely on particular areas or sections of the product to be grasped.
In order that a reliable stacking is achieved for the plastic products in continuous take-over mode, it is provided according to a development of the invention that the gripping members are formed in particular on the stacking and holding device as two-dimensional claw projections with an inner side assigned to the product and a rearward outer side, wherein in the inner side one or more undercuts, steps or depressions are formed as claw elements or shear means. If the two-dimensional extension in the direction of the periphery or outline of the product to be grasped is sufficiently wide or great, channels are then obtained for the products, on the basis of the above-mentioned development of the invention, which ensure a secure and reliable stacking, Stability against shaking and vibrations, as well as against collapse of the stack resulting therefrom, is also promoted.
Irregularities in the shape of the product or the item for stacking may arise during long-term practical operation, in particular in the case of a cup ejected from a mould. This may lead to impairment of the transfer between catching and stacking and holding device, wherein even mutually colliding gripping members of the catching and stacking and holding devices may lead to mechanical damage or deformation, in some cases in operative connection with remaining products or items.
To solve this set of problems, it is proposed according to the invention in the context of the general inventive idea, for a stacking and holding device possessing the features mentioned in the preamble, that the gripping pawl be freely pivotable about an axis which runs parallel with the stacking channel. Due to the free pivotability the gripping pawl may, in order to grasp the item of material, nestle up against its production contour largely snugly or positively. It is no longer necessary during the prior assembly of the stacking and holding device to align the gripping pawl in its exact rotary position, instead this takes place afresh and automatically for each item of material to be stacked. Due to the rotatory degree of freedom about an in particular axis parallel axis of rotation, a stacking channel may be formed which may as it were adapt dynamically to a certain extent to differences in shape of the product for stacking. The stacking channel as it were xe2x80x9cbreathesxe2x80x9d with the shape tolerances arising from mould and catching device and impressed on the item of material to be stacked. The further advantage is obtained that in the event of a collision of a gripping member of the catching device with the claw member or its gripping pawl on the stacking and holding device the gripping pawl may deviate to a certain extent due to corresponding rotation. Thus a collision between gripping members on catching and stacking and holding devices is offset and mechanical deformation of the gripping members is avoided.
For the further dimensional stabilization of the gripping members on catching and stacking and holding device (clamping arbors or claw elements) the gripping pawl is according to an advantageous development of the invention surrounded by a protective wall which is so constructed and arranged at a distance relative to the gripping pawl that the gripping pawl-facing inner side of the protective wall forms a rotation limiting stop with rotation play for the gripping pawl. The gripping pawl is thereby prevented from being able to rotate too far compared with the optimal gripping position and in so doing forming an obliquely positioned obstacle to the incoming product for stacking and deforming the latter mechanically.
According to a further, suitable development the axis of rotation of the gripping pawl is embedded in the protective wall or kept non-rotatable therein and bears on its free end projecting out of the protective wall and parallel with the stacking channel the freely pivoting gripping pawl.
To enable the gripping pawl to have a rotation play relative to the basic body of the stacking and holding device, in particular relative to the protective wall, it is suitable to provide the gripping pawl axis of rotation with stopping means which are capable of being coupled or brought into engagement with the basic body or the protective wall of the stacking or holding device. In order that the stopping means against the gripping pawl axis of rotation may be actuated, it is provided according to an advantageous development of the invention that the protective wall is provided on its inner side (facing the gripping pawl) with an opening or recess leading to the axis of rotation and preferably positioned radially with respect to the stacking channel. In addition, the above-mentioned stopping means for the axis of rotation may be actuated in order to fix them relative to the miscellaneous stacking and holding device equipment.
Within the scope of the general inventive idea for solving the complex set of problems according to the invention it is proposed according to the invention, for a gripping pawl with the features mentioned in the preamble, that the latter be provided with an axis of rotation integral with the body which takes the form of an elongated basic body comprising a top end and a bottom end. To the top end is attached, freely rotatable, a gripping head assigned to the respective product for stacking. At the bottom end and/or also in the central area of the basic body are formed means for stopping against or opposite the stacking and holding device. By means of the latter the gripping pawl axis of rotation may be fixed non-rotatably within the basic body of the stacking and holding device. The gripping head may then rotate to and fro on the axis of rotation or the elongated basic body opposite the other part of the stacking and holding device.
In order that further, flexible degrees of freedom are also provided for the gripping head for the nestling against multifarious shapes and contours of the item for stacking, a development of the invention consists in the elongated basic body being manufactured of elastically and/or springily pliable material. There is formed as it were an elastically pliable stock on which the gripping head may [be] deflected springily through being acted upon by items for stacking and return pendulum-like into its initial position again.
With the structure according to the invention for the gripping pawl, which may be broken down substantially into the gripping head and the elongated, stock-like basic body as axis of rotation, the possibility is created of a further advantageous development, according to which the gripping head may be mounted on the basic body so as to be capable of loosening or detaching and is simultaneously on its gripping inner side adapted in the shape or curvature there to the shape and/or contour of the item for stacking which is to be grasped. The advantage in production and storage terms consists in the fact that there may be retained for the elongated basic body as axis of rotation a standard form suitable for all applications. There may then be fitted to the basic bodyxe2x80x94depending on the form of the item for stackingxe2x80x94differently shaped or constructed gripping heads.
For the realisation of a simple pivoting for the gripping head, it is suitable to arrange the latter so that it is rotatable to and fro on its head end by means of a screw connection. In order that the rotation play is obtained, the gripping head must not be screwed home or tightened on the head end.
A suitable realisation of the stopping means consists in a manually screwable pin with external thread being disposed in an internally threaded bore which is constructed in the central area or at the bottom end of the basic body and passes through the latter at right angles to the longitudinal axis. In order to obtain the rotation play, there is expedient as a further development a screw limiting stop on the basic body for the gripping head. The latter is arranged at a distance measured relative to the screw-in thread at the top end of the basic body (for the gripping head), such that when the gripping head stops or comes to rest against the limiting stop the centre axis of the internally threaded bore runs parallel with a notional straight line which passes at an oblique angle through a lateral surface, assigned to the product or the item for stacking, of the gripping head. In conjunction with the just mentioned screw connection between gripping head and top end, the radial operational opening for the stopping means of the axis of rotation and the above-mentioned rotation-limiting stop, the possibility must be prevented, where rotation play for the gripping head is guaranteed, of the latter being screwed out from the basic body top end. In addition, in order that operation of the stopping means is possible, the centre axis of the internally threaded bore or of the externally threaded pin must lie flush or in a line or congruent with the longitudinal or access direction of the operational opening or recess. Thereby there is always guaranteed, in the case of the last-mentioned development of the invention, the rotation and screw play for the gripping head on the basic body top end.